1. Field of the Invention
The present invention relates to a dye developer and, more particularly, to a dye developer for a light-sensitive material which can provide an image by a diffusion transfer process. More specifically, the present invention is concerned with a novel cyan dye developer to be used in a color diffusion transfer light-sensitive material, whose absorption is shifted to the short wave-length side upon exposure and is altered to the desired hue upon reaction with a processing solution.
2. Description of the Prior Art
Japanese Patent Publication No. 5189/59 describes a process for forming a transferred dye image using a dye developer. The term "dye developer" as used herein means a compound which possesses both a group capable of developing a silver halide emulsion and a dye moiety, and which is immobilized in accordance with the amount of developed silver halide, the rest being transferred to an image-receiving element to provide a transferred image.
When such a dye developer is associated with a light-sensitive emulsion having a substantial spectral sensitivity in the absorption region of the dye developer and disposed thereon on the side to be exposed with respect to this emulsion or incorporated in the same layer, desensitization of the light-sensitive emulsion apparently occurs due to the light absorption of the dye developer itself. In order to prevent this desensitization, Japanese Patent Publication No. 12393/61 describes a means of chemically modifying the dye developer to initially convert the dye developer to a compound having an absorption shifted toward a shorter wave length and restoring the absorption of reaction with a processing solution upon processing. However, this patent describes only magenta dye developers.
Anthraquinone derivatives, phthalocyanine derivatives and bis-azo derivatives have heretofore been known as cyan dye developers. For example, anthraquinone cyan dye developers are described in detail in U.S. Pat. Nos. 3,135,606, 3,209,016, Japanese Patent Publication Nos. 4380/59, 12432/60 and 17243/63, phthalocyanine dye developers are described in U.S. Pat. No. 3,674,478, and bis-azo cyanine dye developers are described in U.S. Pat. Nos. 3,134,762, 3,236,645, 3,142,565, 3,173,906, etc.
However, these conventional anthraquinone, phthalocyanine or bisazo cyan dye developers reduce the efficiency of active light upon exposure due to a filter effect from the light absorption of the dyes themselves, thus reducing the sensitivity of the light-sensitive material. Also, enhancing the sensitivity of a silver halide emulsion to obtain a highly sensitive light-sensitive material tends to cause a reduction in image density and to make the light-sensitive material itself unstable.
In particular, with conventional bis-azo cyan dye developers, the hue possesses an absorption maximum at not more than about 600 m.mu. and therefore a desirable image having an absorption maximum at not less than about 600 m.mu. cannot be obtained.
Also, with conventional anthraquinone cyan dye developers, the extinction coefficient of image formation is so low that the optical density tends to be insufficient unless these dye developers are employed in a large amount. On the other hand, conventional anthraquinone and phthalocyanine cyan dye developers have the defect that a slight modification of the chemical structure thereof is difficult and a chemical structure showing optimum photographic properties is difficult to synthesize.